Introduction
Transportation consumes a lot of energy and it is not easy to curb energy use or develop ways to move away from fossil fuels. People value the freedom of private transport and find it difficult to reduce their dependence and instead embrace public transportation. We will consider the energy used moving freight and goods, and if the engine can be made more efficient, or modified to work on different principles that are less energy wasteful.
Personal Transportation
Road transport uses around 20% of the energy consumed in the UK. But, because of a long chain of overheads and inefficiencies, only a few percent of the primary energy, the total energy contained in the fuel consumed, ends up moving the actual ‘payload’. There is clearly scope for a significant improvement in energy efficiency. However, many of the measures being proposed target personal transport and view the motor car merely in the context of mobility and fail to recognise the iconic role of the automobile in a modern consumer society.
For this reason some of the actions being suggested to curb excessive use will tend to fail. Car pooling, for example: Personal transportation is convenient, perhaps even essential, and a car is mainly purchased for the benefit of the individual or family. The car owner does not expect to be inconvenienced, and car sharing is no more (or less) feasible than house sharing.
Cars maximise the use of time, and though it is recommended that short journeys be made on foot, valuable time is lost as a consequence.
Figure 1: Automobile, also called motorcar or car, a usually four-wheeled vehicle designed primarily for passenger transportation and commonly propelled by an internal-combustion engine using a volatile fuel. [source] used under fair dealing.
Transportation is one of the largest sectors of the global economy. It is also one that is changing rapidly. Smartphones and Internet-based technologies have helped launch and enable new business models like Uber, Lyft, and car2go. Even self-driving cars are no longer science fiction. But the future of transportation — what we call mobility — will go far beyond these developments.
In spite of congestion, worldwide car sales are still rising. The growth in car use tends to proceed in explosive phases: the launching of the low cost Model T Ford after WW1; the Volkswagen Beetle in Germany during WW2, the people’s car; and now the projected massive sales in India and China as these economies continue to grow. It is possible this growth will continue unabated until the motor car is either too inconvenient or too expensive. There is little that can be done to ease traffic congestion because the road system is essentially two-dimensional, and prioritising public transport by reserving network space makes the situation worse for the private car owner. Parking is an additional difficulty. Especially in congested areas such an cities. With the ever improvements to electric vehicles, the next issue alongside traffic congestion will be parking for the recharging stage of travel—development and electricity costs, and available space.
The polluting gases produced by cars are already a problem and the problem is likely to increase. Can the world rely on increasing fuel cost to limit car use? Currently in 2021, fuel prices sit around £1.35 per litre with some difference between Petrol and Diesel. Premium fuels tend to be higher, around £0.10-0.50 more. Fuel prices are still not high enough to moderate demand, but the accepted rules of economics would suggest that prices will continue to rise until demand falls.
Activity 1
- What common-sense measures can be taken to reduce the fuel consumed by a car (whilst retaining the freedom it offers)?
- What forms of research can be made to improve fuel efficiency?
Solution
a.
Some measures that can be taken are;
- Weight reduction
- Reducing resistance or friction
- Avoiding speed changes or idling
- Optimise travel route
- Unused items should be removed from the car
- Maintain the tyre pressure at the correct level
- Replace filters and regularly service the car
- Use the recommended fuel in the car
- Combine a lot of short trips into one longer journey
- Don’t drive with the windows open or the air conditioning on
- Do not drive erratically
- Drive in the correct gear
b.
Much of this research focuses on technologies that can improve the efficiency of a variety of vehicles, including internal combustion, alternative fuel, and plug-in electric vehicles. Areas to improve overall vehicle fuel economy and reduce emissions are:
- Combustion engine research focuses on improving new combustion strategies that can greatly improve engine efficiency and minimize the emissions formation in the engine itself.
- Emissions reduction research focuses on reducing the cost and improving the efficiency of aftertreatment technologies that reduce exhaust emissions. Including software to help calculate greenhouse gas and other emissions.
- Fuel effects research focuses on better understanding how fuels from new sources can affect advanced combustion systems.
- Idling reduction work focuses on minimizing unnecessary idling from vehicles.
- Light weighting research focuses on lowering the cost and improving the performance of lightweight materials like high-strength steel, aluminium, magnesium, and carbon fibre.
- Aerodynamics and other parasitic loss research focuses on reducing the energy lost to non-engine sources such as drag, braking, rolling resistance, and auxiliary loads like air conditioning.
Freight Movement
Energy is consumed moving products and goods from manufacturer to consumer, conveniently and unseen, and in an age of globalisation the market for many products now spans the entire planet. Information technology in many ways helps mitigate the impact of carbon emissions and transport congestion, but also makes trade and communication cheaper and easier, sometimes with negative consequences. Using the Internet, the customer can source products anywhere in the world at the best price. There is huge choice and the growth in demand means the movement of goods is increasing dramatically, and items are moving ever greater distances. A website like eBay is an effective mechanism for recycling and reuse, but the penalty is additional energy used moving goods about, more energy in some cases than was originally required in manufacture.
But only a fraction of goods will ever be ‘mail order’. Food is moved about the UK in vast quantities, often in refrigerated containers, in order to offer maximum customer choice (Fig. 2), but the centralisation and concentration of sales in supermarkets is also increasing our dependence on the motor car.
Whilst supermarket chains are certainly driven by economic expediency in what is a very competitive sector, there is evidence of a desire to display social corporate responsibility. Efforts are being made to reduce the environmental impact of food sales by broadening the supply chain, for example by sourcing locally from suppliers who do not necessarily offer the lower cost and uniform quality associated with mass production.
The concept of food miles is applied as a measure of the carbon impact of different food types. In the UK, food transport accounts for 25% of all Heavy Goods Vehicle (HGV) kilometres in the UK, producing near 20 million tonnes of CO2 annually—equivalent to around 5.5 million typical cars. Airfreight generates 50 times more CO2 than sea shipping. But sea shipping is slow, and in our increasing demand for fresh food, food is increasingly being shipped by faster and more polluting means.
Moving the same weight of goods an equal distance by rail rather than road is less environmentally damaging, with only one-fifth of the greenhouse gas emissions of lorries. Whilst sea and rail can only deliver between ports or stations, and not point-to-point, the universal adoption of containers means that transfer for the final road connections can be made with ease and should not be an impediment to greater use of rail and sea routes for freight movement.
Figure 2: Annual HGV flows on the GB road network, 2016 [source] (public domain)
But in spite of the existing benefit of rail over road, there are still ways that rail can improve (Fig. 3). More line electrification can increase efficiency and enable regenerative braking can be adopted: Instead of using friction to slow down the train (and producing unusable heat), the train is slowed by reversing the motor and allowing the forward momentum to generate electricity which is then transferred back onto the overhead line. Regenerative braking can lead to a saving of 20% on the energy consumed. Rail efficiency in general can be improved a further 20% by adopting such measures as switching off electric trains at night, matching train length to capacity, reduce idling, and weight and drag reduction.
If many more passenger and freight road journeys were to be displaced to the railways, the benefit would not necessarily include reduced road congestion; the number of cars on the road might merely expand to fill up the released capacity.
Figure 3: UK Rail Routes with colour coded traffic [source] used under fair dealing.
Container vessels navigate the ocean like trucks on busy highways, following specific shipping routes (Fig. 4) to and from the world’s busiest seaports. These routes support international trade by offering the fastest sailing times for ships carrying the goods we use and rely on every day.
Figure 4: Global Shipping Routes with Traffic Frequency ranging from green (less) to red (more) [source]. used under fair dealing.
The English Channel
Each day, more than 500 vessels cross the 350-mile-long English Channel — widely considered the busiest shipping lane in the world and a critical route in the European shipping network. Cargo vessels, carrying everything from oil to wheat, share the channel with passenger ferries, fishing vessels, pleasure craft and even the occasional swimmer.
Activity 2
- How efficient is it to move freight by sea compared to overland by air?
- Identify insights into the future of freight transport?
Solution
a.
Sea freight is very slow, but remarkably, in spite of the friction encountered by a vessel moving through water, transferring freight by sea is relatively efficient. One of the main reasons for this is that ships move very slowly, generally at a speed of between 10 and 20 mph, and because resistance is proportional to velocity, frictional losses are lower. Ships do not move against gravity, and will not accelerate or decelerate by any significant amount. The losses will be similar no matter the weight of the ship. When a boat is completely filled with cargo, the ratio of goods to boat weight is high and energy is used efficiently. For these reasons, the additional friction that certainly exists when moving through water is not a problem.
Similar to air freight, sea freight can be delayed due to a range of different reasons, the same reasons in fact as air freight – bad weather conditions, strikes, traffic congestion at the harbour, labour strikes and documentation difficulties at customs clearance. Flights usually go according to schedule and in case of delays, shipments can be rerouted or rescheduled to a later flight most commonly the same day. When it comes to sea freight, delays usually count in days. In addition, unlike flights, ships are often off schedule. Switching to sea freight is thus not necessarily a good choice in terms of quality improvement or quality innovation.
Usually, sea freight is less costly than air freight. For smaller shipments, however, air freight can come out as cheaper. As space is limited in an aircraft, goods will be priced according to necessity for air transport. When shipping less than a container, the cost is calculated in cubic meters. If your shipment is small, air transport might in fact cost you less. It could also still be more expensive, but with a smaller difference between the two, you might prefer the safest alternative, which, for sensitive products, is air freight.
Another thing that must be taken into account is the cost of capital. As mentioned before, long sea transports are not suitable for products with a short shelf life, especially as sea freight is more prone to delays. lengthy transports will delay sales, thereby binding up capital that could be put to other use. Thus, whether sea or air is the better choice depends on many factors – the risk profile of the product, shelf life, warehousing at the airport/seaport and cost of goods (capital bound up in transport) among other things.
b.
- Regulation, particularly in relation to environmental emissions
The major focus of regulation is on reducing the emissions of environmental pollutants from HGVs at a local level, and this has been driven by EU emissions standards legislation. HGV’s are gradually becoming cleaner as companies increasingly purchase new HGVs which have to conform to Euro 6 standards.
Use of electric vehicles (EVs) for deliveries and collections from urban distribution centres (UDCs), which are large-scale consolidation centres that receive goods and then consolidate them into full loads for last-mile deliveries by EVs.
Development of smaller-scale road-only consolidation centres on the edge of smaller urban areas to allow the transfer of goods from larger freight vehicles into smaller electric vehicles for final delivery.
- Alternative fuel technologies
Given the ambition to limit the sale of new diesel and petrol cars and LGVs, it seems increasingly likely that there will gradually be a greater take-up of electric LGVs at a national level for relatively short-distance flows, but unless there is a step-change in battery technology, or advances in other alternative fuel solutions such as hydrogen fuel-cells, this is most likely to be for deliveries from distribution centres located close to the major conurbations rather than to towns and cities in more peripheral locations.
Furthermore, existing battery technology is significantly heavier when compared with a tank of diesel fuel. This eats into the gross laden weight, thereby reducing a vehicle’s payload capacity. In order to encourage greater use of electric HGVs, the gross weight regulations may need to be amended to allow for heavier electric HGVs that are able to carry the same payload capacity when compared with a diesel vehicle
- Autonomy and automation
Introduction of ‘platoons’ of HGVs that travel together on the strategic highways network and provide fuel efficiencies to road hauliers due to the reduction of drag. These would not be genuinely autonomous vehicles because they would still require a driver to be located in each cab for the departure and the final approach to the destination. Without significant technological improvements it seems likely that these platoons would be restricted to use on motorways and dual carriageways so that there are opportunities for overtaking and to ensure safety.
- Infrastructure pricing and land use planning
Capacity on the road network, particularly during the peak periods, is a scarce resource and, at the same time, road freight may not be paying for the full costs it imposes on society which include not only the impact on congestion but also the cost of environmental emissions and accidents.
The introduction of a system of infrastructure charging for both freight and passengers. This could involve re-distributing the existing taxation imposed on the different modes of transport and applying additional charges where justified – using a distance-based system which could take account of the time of day, the specific section of the network and the type of vehicle as well as the distance travelled.
Such an approach to infrastructure charging would help to ensure that the private sector invests in key freight infrastructure, such as distribution parks and Strategic Rail Freight Interchanges, in competitive locations. However, this will only be possible if the land use planning system is able to bring forward large sites in competitive locations, and this may require a more strategic approach to the selection and promotion of nationally significant sites by Government.
Public Transport
Passenger car journeys currently account for 78% of vehicle-kilometres travelled and 61% of emissions in the UK. Reducing demand for car travel offers significant potential for reducing emissions, with associated benefits for congestion, air quality and health. Four factors that could contribute to a reduction in private car travel are;
- Societal and technological changes; This includes factors such as increased home-working, increased use of IT and technology and continuing trends towards greater use of internet shopping.
- Increase in car occupancy; Shared mobility (e.g. shared cars and shared trips) can also reduce car travel demand.
- Modal shift to active travel; Walking and cycling trips have increased while trips taken by bus have declined. Assuming that 5-10% of people working live within near proximity of work, car journeys could be shifted to walking and cycling. This could reduce emissions and congestions.
- Modal shift to public transport; There is scope to switch some car journeys onto appropriate public transport, particularly in urban areas. Bus routes are likely to be within walking distance of the majority of homes and work placements so is a significant option as an alternative mode of transport.
Huge reductions in energy use can be achieved by persuading the majority of the population to adopt public transport instead of personal vehicles. An extensive, reliable, integrated public transport system with frequent services reaching all areas of every community is a necessity, and only the very basic infrastructure is established in the UK. However the network even as it stands is for the most part underused. In some cities a good public transportation system emerges as a necessity out of a chaotic road network, otherwise the city could not function, e.g. London.
Figure 5: Compares for passenger capacity of different modes of transport in terms of passengers per hour on a 3.5 m wide lane [source] (public domain)
It is obvious that a reasonably priced well-run public transport system must be in place before people will reduce car use, and there is little point in pressurising car users to adopt public transport until this is the case. However, in common with all other activities needed to reduce green house gas emissions, there is a high initial capital cost in setting up a modern transit system that goes well beyond the basic infrastructure that currently exists. Nevertheless public transport use can be increased by steadily improving the system and responding to the views of the travelling public.
There has been little change over time in domestic transport emissions, either by mode or across the sector. The data in Fig. 6 (and caption link) suggests that domestic transport carbon dioxide emissions have fallen 19.6% since 2019, to 97.1 million tonnes in 2020. This is associated with falls in transport usage during restrictions introduced in response to the COVID 19 pandemic. These estimates also suggest that domestic transport carbon dioxide emissions were 23% below the 1990 figure. A key point to consider is that public transport, other than taxis, is considerably lower that personal transport.
Figure 6: Greenhouse gas emissions by transport mode, 1990 and 2019.[source] (public domain)
Referring to Fig. 7, the remaining emissions are shared between vans (17%; 20 MtCO2e), buses (3%; 3 MtCO2e), rail (2%; 2 MtCO2e) and other surface vehicles (1%; 0.9 MtCO2e).
Figure 7: Breakdown of surface transport sector emissions [source] (public domain)
The number of rail journeys is increasing, largely because the journey time can be less than the same trip by road and the degree of comfort is generally good. Currently, rail is significantly let down by the routing network—set to a specific route which has limited access. An expansion of the rail network is therefore a crucial way to significantly increase public transport use.
Activity 3
- What regulatory tools act to limit car use?
- Increasing the scope and capacity of the UK rail network is necessary for the future, discuss actions involving the High-Speed Railways, e.g. High Speed 2 (HS2)
Solution
a.
There are a number of measures that limit the freedom of the car user, but many of these are management actions that make the system operate effectively. This includes speed limits and restrictions, and traffic flow control. There are also unintentional measures such as decisions taken on new road construction to ease congestion (or not), and the timing and duration of road works. Raising fuel duty sharply would probably be an effective regulatory measure, if the hike were large enough, but might be politically suicidal at a time when rising oil prices are already driving fuel costs sharply upwards.
One acceptable regulatory mechanism is the level of road tax (vehicle excise duty). By making road tax cheap for small cars and expensive for big cars, this is a clear incentive to move to less polluting cars. Congestion charges, parking charges and toll roads are also very effective deterrents.
b.
Much of the UK’s rail network was built over 100 years ago. Rail travel has more than doubled over the last 20 years. The planned development of new high-speed rail networks – of which High Speed 2 (HS2) is the best known and most advanced – also has the potential to make a significant difference to capacity on some of the most heavily-utilised routes in the country. HS2 Limited is the company responsible for developing and promoting the UK’s new high speed rail network. It is funded by grant-in-aid from the government.
HS2 is one of the best options for taking the pressure off the existing transport sector as it adds extra capacity where it is needed most. Building HS2 frees up a massive amount of space on the existing railway by placing long distance services on their own pair of tracks. Once HS2 is operating, services can run much closer together, meaning there can be more rush hour trains, helping to relieve overcrowding.
Rail is by far the most carbon efficient mass transit transport system available. HS2 trains will serve over 25 stations, from Scotland to the South East. They include eight of Britain’s ten largest cities, carrying over 300,000 people a day or 100 million passengers a year.
HS2 trains will be highly energy efficient and powered by a grid that uses increasing amounts of energy from zero carbon sources.
Figure 8: The new HS2 rail network [source] (public domain)
Many features of the new railway, such as tunnels, bridges, viaducts and underpasses, have been included to minimise or reduce environmental, noise and visual effects. Whilst the construction of these will inevitably create carbon emissions, there are commitments to minimise the overall carbon footprint. For e.g. HS2 is also pioneering a low carbon concrete to reduce construction carbon emissions. It lowers carbon dioxide by 42%. Residual carbon is then offset to meet the Carbon Neutral Protocol.
The roll-out of the Digital Railway programme has the potential to significantly aid in catering for this growth by increasing capacity in the network. The European Railway Traffic Management System (ERTMS) will introduce a new approach to signalling, which will allow far more trains to be safely run over the same length of track and require significant additional ongoing cooperation between train operator and infrastructure provider.
Engine and Vehicle Development
Given the difficulty in achieving any reduction in car use, an alternative approach is to make vehicles use fuel more efficiently. The combustion engine and even the form of the car itself can be modified in a number of ways to improve efficiency, and give a better miles per gallon (mpg) mileage performance (note that the imperial unit is preferable in this case to the SI unit — litres per kilometre — because it is a measure of car performance that everyone understands).
The reason why a vehicle consumes fuel is two-fold. As speed increases, the kinetic energy rises and this energy must be supplied by the engine. The kinetic energy is proportional to mass, hence a lighter, unloaded vehicle will use less fuel accelerating (Fig. 9). Energy is also lost by a moving car through frictional contact with air molecules and in the contact with the road. Fuel can be saved by making the car aerodynamic in shape to reduce the air turbulence that increases friction, and by keeping tyres at the correct pressure to reduce slippage. However, for safety it is better to have “stickier” tyres with a higher friction coefficient to improve drive-ability. A vehicle with smooth tyres are unsafe unless for purposely designed purposes, e.g. motorsport racing.
Figure 9: Relationship between car mass and efficiency mpg, with Highway (green) and City (blue) comparison. [source] (CC0)
Energy can also be saved by avoiding idling, i.e. keeping the engine running whilst disconnected from the drive system, and trying to keep the engine running at its optimal firing frequency. Also avoid braking as much as possible.
But no matter what measures are taken, the thermodynamic operation of the internal combustion engine means that a maximum of 25% of the energy in the fuel can be converted to work. In contrast, an electric motor can convert electricity to kinetic energy with better than 90% efficiency. But an electric vehicles would require sufficient battery storage to give an acceptable range on full charge of perhaps 300-400 miles. In spite of improved efficiency and the ability to use regenerative braking to recover energy, a lot of batteries are required. These are expensive and heavy, but battery technology is continuously improving.
Hybrid vehicles have an electric motor, but also use a conventional engine as backup (Fig. 10).
Figure 10: The plug-in hybrid vehicle [source] (public domain)
It has the advantage that the electric motor can operate in stop-go driving and the engine is used for motorway or highway driving. The technology is complex and expensive and because the engine charges the batteries, it is not guaranteed that the fuel savings of about 20-30% will ever cover the capital cost — the same old problem with energy saving technologies.
Power can also be generated onboard using stored hydrogen to create a Fuel Cell Electric Vehicle, FCEV (Fig. 11). A fuel cell can be very small and produces electricity with a theoretical efficiency approaching 90%, though in practice the efficiency is around 60% and there exists the problem of storing the significant quantity of hydrogen gas required to ensure a reasonable range. In spite of these problems, this is a promising technology, not least because hydrogen can be produced from intermittent renewable sources and stored indefinitely. There are a number of hydrogen vehicle available on the market, but the refuelling infrastructure is very limited.
The hydrogen vehicle can be termed a Zero Emission Vehicle (ZEV), providing the hydrogen is produced using a renewable source of electricity.
There is little doubt that changes in vehicles or how they are used is necessary. It is considered unacceptable to maintain the status quo using biofuels because of the environmental damage and rising food costs.
Figure 11: The hydrogen fuel cell electric vehicle (FCEV) [source] (public domain)
Activity 4
- How much energy would a 1 tonne vehicle require to reach a speed of 60 mph from stationary? Approximately how much energy is lost at this speed because of friction?
- How much energy does an airplane weighing 80 tonnes consume climbing to 5,000 metres?
Solution
a.
The kinetic energy (KE) of the vehicle at 60 mph must be supplied by the engine:
KE = ½mv2
where the mass (m) is 1,000 kg, and the velocity (v) is 60 mph.
To get a sensible result in Joules, the units have all got to be SI, i.e. metres, seconds, kilograms. 60 mph is equivalent to 0.45 x 60 = 27 m s-1. Inputting values into the equation, we get:
KE = 0.5 x 1,000 x 27 x 27 J = 364.5 kJ
In kWh, 364.5 / 3.6 = 0.1 kWh
The conversion to kWh is achieved by dividing by 3.6 MJ. It is clear therefore why town driving uses so much fuel. If one brakes and accelerates frequently a lot of energy is used. Accelerating 10 times will require 1 kWh of energy, and a quantity of fuel with 3 kWh of primary energy is needed (because the engine will be no more than 33% efficient). Thus 0.25 litre of fuel may be consumed in just a few minutes.
The energy lost due to friction depends on the shape of the car. A good aerodynamic car will look uninteresting, like it was squeezed out of a tube. But aerodynamics are damaged by choosing form over function in order to sell the car.
Off topic as an additional part to the question. Typically, at 60 mph, a car presenting an area of 1.2 m x 1.2 m into the flow and having a drag coefficient (Cd) of 0.1 will apply a retarding force of ½ρCdv2A. Slotting in the numbers (where ρ is the air density and A is the area of the car), we get a force of;
FR = 1/2 x 1.204 x 0.1 x 272 x 1.44 = 63.2 N
The energy expended each second maintaining the same speed is the force times the distance;
E = F d = 63.2 x 27 = 1706.4 J
In fact actual energy losses are six times this in practice because of engine friction, rolling resistance and undulations, and the engine is likely only 25% efficient at that speed. The energy consumed in 1 hour is;
E per hour = 3600 x 6 x 1706.4 x 4 J = 147 MJ, or 0.7 gallon of fuel.
b.
The energy required to work against gravity is
E = m g h = 80,000 x 9.81 x 5,000 = 3.924 GJ
This is about 0.1 toe, but because of engine inefficiency (30%) and air friction, 0.5 toe or about 500 litres of fuel may be used reaching cruising altitude.
Air friction is much reduced at higher altitudes and some of the potential energy can be converted to horizontal thrust as the plane descends.
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